Asphalt is a common material utilized for the preparation of paving and roofing materials and also for coatings such as pipe coatings and tank liners. While the material is suitable in many respects, it inherently is deficient in some physical properties which it would be highly desirable to improve. Efforts have been made in this direction by addition of certain conjugated diene rubbers, ethylene containing plastics like EVA, and polyethylene, neoprene, amorphous polyolefins, resins, fillers and other materials for the modification of one or more of the physical properties of the asphalt. Each of these added materials modifies the asphalt in one respect or another but certain deficiencies can be noted in all modifiers proposed. For example, some of them have excellent weather resistance, sealing and bonding properties but are often deficient with respect to warm tack, modulus, hardness and other physical properties; and some of them improve only the high temperature performance of asphalt, some only improve the low temperature performance of asphalt, while some lack thermal stability or mixing stability with asphalt.
Since the late 1960s, diene polymer rubbers such as styrene-butadiene rubber and styrene-rubber block copolymers such as styrene-butadiene-styrene and styrene-isoprene-styrene block copolymers have been used to dramatically improve the thermal and mechanical properties of asphalts. Practical application of the rubber addition approach requires that the blended product retain improved properties and homogeneity during transportation, storage and processing. Long term performance of elastomer-modified asphalts also depends on the ability of the blend to maintain thermal and chemical stability.
Such polymers have been found to be very advantageous but in some end uses, such as roll roofing membranes, high processing viscosity of blends of asphalt and such polymers leads to reduced manufacturing rates. Other attempts at lowering the processing viscosity, such as reducing molecular weight or polymer content or adding oil, have proved to be undesirable because the softening point of the composition was lowered to such an extent that adequate slump resistance could not be achieved. Also, the processing stability of blends of some of the commercially used polymers could advantageously be improved to provide a wider processing window. Hydrogenated versions of styrenic block copolymers provide greatly improved processing stability.
Styrenic block copolymers are widely used as asphalt modifiers for roofing and paving applications. Since asphalt can vary significantly in its chemical composition and molecular weight distribution, asphalt modifiers must either be supplied for specific asphalts or a modifier must be found that has utility over as wide a range of asphalt properties as possible. In particular, styrenic block copolymers tend to be incompatible with asphalts which have a high asphaltenes content. One compound which is compatible with such asphalts is a compounded blend of a styrenic block copolymer which is optionally hydrogenated, a naphthenic oil, and carbon black.
Mixtures of three components which have not been compounded by melt processing do not provide improved compatibility. Such compounds are disclosed in U.S. Pat. No. 5,036,119 the disclosures of which are herein incorporated by reference. The naphthenic oil is required because of the high melt viscosity of styrenic block copolymers, especially in the presence of carbon black. Typically compounds of high molecular weight styrenic block copolymers require the addition of oil to avoid unacceptable degradation or melt fracture during processing. A high level of oil is undesirable in applications which are highly sensitive to bleeding of the oil or where the oil causes unacceptable loss of high temperature properties.
Other polymers are currently used for asphalt modification including amorphous polyolefins, especially high molecular weight atactic polypropylene. Atactic polypropylene has advantages in processability and high temperature performance but requires higher addition levels than styrenic block copolymers. Lower molecular weight amorphous polyolefins do not have the strength or elasticity of styrenic block copolymers. It would be advantageous to produce a composition which combined the advantages of styrenic block copolymers and amorphous polyolefins and minimized their individual disadvantages. It has not been possible to create such compositions using conventional unhydrogenated styrenic block copolymers because they are incompatible with amorphous polyolefins. Blends of unhydrogenated styrenic block copolymers, amorphous polyolefins, and asphalt typically exhibit unacceptably poor phase stability during processing and long term performance.
Single ply membranes are widely used in the roofing industry. They are commonly produced from EPDM, PVC, and CSPE. EPDM makes thermoset single ply membranes which require careful cleaning and adhesive application to seal the seams. PVC and CSPE make thermoplastic single ply membranes which have environmental problems because the polymers are chlorinated.
Thus it can be seen that there is a need for a styrenic block copolymer compound that is easily processable, highly compatible with asphalt, and oil free to minimize bleeding and maximize high temperature properties. There is also a need for a method to compatibilize blends of unhydrogenated styrenic block copolymers and amorphous polyolefins. There is also a need for a method to compound high molecular weight styrenic block compounds, especially in the presence of carbon black, without the addition of oil. There is also a need for a thermoplastic, weatherable single ply roofing membrane which has minimal environmental problems. There is also a need for such a compound with enhanced weatherability. The present invention provides compounds which meet all these needs.